I'm on left, alyse on right (as you lie on your back on the bed), except this gets trumped if the bed is up against the wall, in which case, alyse gets open side, I get closed side, because she tends to get up in the middle of the night more than I do.

This also gets trumped if one side has light shining on it due to curtain weirdnesses -- I get dark side, she gets light side.

So I think it's a default case that gets trumped by our own frailties. :)